Benzo[b]fluoranthene is one of over 100 different polycyclic aromatic hydrocarbons (PAHs). PAHs are chemicals that are formed during the incomplete burning organic substances, such as fossil fuels. They are usually found as a mixture containing two or more of these compounds. It is one ingredient of cigarette. (4)

The ability of PAH's to bind to blood proteins such as albumin allows them to be transported throughout the body. Many PAH's induce the expression of cytochrome P450 enzymes, especially CYP1A1, CYP1A2, and CYP1B1, by binding to the aryl hydrocarbon receptor or glycine N-methyltransferase protein. These enzymes metabolize PAH's into their toxic intermediates. The reactive metabolites of PAHs (epoxide intermediates, dihydrodiols, phenols, quinones, and their various combinations) covalently bind to DNA and other cellular macromolecules, initiating mutagenesis and carcinogenesis. (4, 5, 2, 3)

Metabolism

PAH metabolism occurs in all tissues, usually by cytochrome P-450 and its associated enzymes. PAHs are metabolized into reactive intermediates, which include epoxide intermediates, dihydrodiols, phenols, quinones, and their various combinations. The phenols, quinones, and dihydrodiols can all be conjugated to glucuronides and sulfate esters; the quinones also form glutathione conjugates. (4)

PAHs are released into the environment via the combustion of fossil fuels, coke oven emissions and vehicle exhausts, as well as naturally from forest fires and volcanic eruptions. PAHs from these sources may contaminate nearly water systems. They are also found in coal tar and charbroiled food. (4)

Minimum Risk Level

Not Available

Health Effects

PAHs are carcinogens and have been associated with the increased risk of skin, respiratory tract, bladder, stomach, and kidney cancers. They may also cause reproductive effects and depress the immune system. (4)

Symptoms

Acute exposure to PAHs causes irritation and inflammation of the skin and lung tissue. (1)

Treatment

There is no known antidote for PAHs. Exposure is usually handled with symptomatic treatment. (4)

Targets

Ligand-activated transcriptional activator. Binds to the XRE promoter region of genes it activates. Activates the expression of multiple phase I and II xenobiotic chemical metabolizing enzyme genes (such as the CYP1A1 gene). Mediates biochemical and toxic effects of halogenated aromatic hydrocarbons. Involved in cell-cycle regulation. Likely to play an important role in the development and maturation of many tissues

Catalyzes the methylation of glycine by using S- adenosylmethionine (AdoMet) to form N-methylglycine (sarcosine) with the concomitant production of S-adenosylhomocysteine (AdoHcy). Possible crucial role in the regulation of tissue concentration of AdoMet and of metabolism of methionine

Transcription activator that binds to antioxidant response (ARE) elements in the promoter regions of target genes. Important for the coordinated up-regulation of genes in response to oxidative stress. May be involved in the transcriptional activation of genes of the beta-globin cluster by mediating enhancer activity of hypersensitive site 2 of the beta-globin locus control region.